Cambridge Assessment International Education Cambridge Ordinary Level

Cambridge Assessment International Education Cambridge Ordinary Level

CHEMISTRY Paper 2 Theory MARK SCHEME Maximum Mark: 75

5070/21 October/November 2017

Published

This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners' meeting before marking began, which would have considered the acceptability of alternative answers.

Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers.

Cambridge International will not enter into discussions about these mark schemes.

Cambridge International is publishing the mark schemes for the October/November 2017 series for most Cambridge IGCSE?, Cambridge International A and AS Level components and some Cambridge O Level components.

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This document consists of 9 printed pages.

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5070/21

Question

A1(a)(i) krypton/Kr (1)

A1(a)(ii) A1(a)(iii)

nitrogen/N2(1) calcium/Ca (1)

A1(a)(iv) copper/Cu (1)

A1(a)(v) chlorine/Cl2 (1)

A1(b)

33S 25Mg2+

number of electrons 16 (1) 10 (1)

Cambridge O Level ? Mark Scheme PUBLISHED Answer

number of neutrons 17 (1) 13 (1)

October/November 2017

Marks 1 1 1 1 1 4

Question

Answer

A2(a) arrangement: ordered/lattice/regular/layers/uniformly arranged/repeated pattern (1)

type of force: electrostatic (1)

A2(b) solid: ions cannot move (1)

aqueous: ions can move (1)

A2(c)(i) (ionisation of) water (1)

A2(c)(ii) A2(c)(iii)

4OH- O2 + 2H2O + 4e- (1) hydroxide (ions) lower in reactivity (than sulfate (ions))/sulfate (ions) less easily oxidised (than hydroxide (ions)) (1)

A2(d)(i) H+, OH-, SO42-, Cu2+ (1)

Marks 2

2

1 1 1 1

? UCLES 2017

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5070/21 Question

Cambridge O Level ? Mark Scheme PUBLISHED

Answer

A2(d)(ii) hydroxide removed (1)

idea of H+ remaining (causing acidity) (1)

A2(d)(iii) Cu2+ ions removed (at negative electrode) (1)

A2(e)

two pairs of bonding electrons (1) rest of structure correct (1)

Question

A3(a)(i) Any two of:

reference to layers (1)

A3(a)(ii)

(layers) slide (1) mobile electrons/electrons can move (1)

A3(b) silver < iron < titanium < calcium (1)

A3(c)(i)

mol Fe2O3 =

14.4 160

OR 0.090 (1)

mol Fe = 2 ? 0.090 OR 0.180 (1)

mass = (0.180 ? 56) = 10.1 (1)

A3(c)(ii)

mol CO2 =

3 2

? 0.18 OR 0.27 (1)

volume = 0.27 ? 24 = 6.48 (dm3) (1)

Answer

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October/November 2017

Marks 2

1 2

Marks 2

1 1 3

2

5070/21 Question

Cambridge O Level ? Mark Scheme PUBLISHED

Answer

October/November 2017

Marks

A4(a) alcohol (1)

1

A4(b) propanol (1)

2

reflux/heat (with sulfuric/strong acid/conc acid) (1)

A4(c) bromine decolourised by fumaric acid/colour of bromine goes (brown to) colourless with fumaric acid (1)

2

no colour change with malic acid/bromine remains brown with malic acid/bromine remains the same colour with malic acid (1)

A4(d)(i) addition (1)

2

condensation (1)

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5070/21 Question

Cambridge O Level ? Mark Scheme PUBLISHED

Answer

A4(d)(ii) for addition polymer:

HO

O

C H H OH

HCCCCH

H OH C H

HO

O

two (or more) repeat units with single bonds between carbon atoms (1)

continuation bonds dependent on correct structure (1)

OR

for condensation polymer:

O

O

H O

CO

CH

CC

CC

H

HH

H

two (or more) repeat units with ester link and continuation bonds (2)

if 2 marks not awarded, 1 mark for ester link drawn correctly

? UCLES 2017

Page 5 of 9

October/November 2017

Marks

2

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